A marker on the rat allows the motion of its head to be imaged by a PET scan.

Image: The University of Sydney

A way of performing PET scans on laboratory rats that are in motion is more accurate and makes possible new experiments linking brain and behavioural function.

The foundation technology has been developed by researchers at the University of Sydney's School of Physics and Brain and Mind Research Institute as reported in the Journal of the Royal Society Interface on 20 June.

"Animal imaging such as positron emission tomography (PET) is almost always performed using anaesthesia to keep the animal still because any movement prevents useful three-dimensional PET images from being reconstructed," said Andre Kyme, who did the research as part of his PhD under the supervision of Associate Professor Roger Fulton.

Even a small amount of motion results in images becoming blurred and prevents useful conclusions about the process being studied.

"Anaesthetising animals is a problem for two reasons: anaesthetic drugs can change what's measured in the brain, and having the animal asleep prevents us from being able to image what's happening in the brain while the animal is fully responsive and able to behave normally," Andre Kyme said.

The non-invasive new method used by the researchers involves tracking an animal's head motion at 30 frames a second then correcting for the motion so that the PET scanner is 'unaware' that the animal moved.

As reported by the ABC the rats "wear a marker on their heads tracked by two cameras linked to a computer, which then processes the movements and accounts for these in the PET scan. The researchers showed the system could be used to track the head of a rat while their body was kept still in a tube inside the scanner, or as it was free to move around a small box designed to fit in the scanner."

The study provides evidence that rats which are awake and unrestrained, especially those able to behave normally, can have their motion tracked relatively simply and inexpensively. The conclusion is that compensating for the motion of awake rats, even those which are completely free to move and behave normally, is now viable.

"All the data collected is adjusted, based on the motion we've measured, so that useful 3D images can be reconstructed. Many powerful experiments to study brain function and correlate it with animal behaviour become possible if animals can be imaged while awake and unrestrained," Kyme said.

"For example, suppose we wanted to study which parts of the brain were most active when an animal was performing a specific task, or compare brain function with and without social interaction - these things are currently not possible using PET. The study of diseases such as Parkinson's and schizophrenia are among the areas of mental health which could potentially benefit.

"It is widely accepted amongst researchers that being able to study an alive and awake animal through imaging would be a great milestone. We're trying to enable data from animal imaging to be more useful and more powerful than it has been, and better able to translate what's happening in the animal to humans in the clinic."